1. Field of the Invention
The present invention relates to an electronic endoscope system that acquires images from inside of a test subject through an electronic endoscope. The present invention also relates to an image processing method for the electronic endoscope system.
2. Description of the Related Art
In the medical field, electronic endoscopes have been widely used for diagnoses, surgical procedures and treatments. Many of the electronic endoscopes conventionally project white light (hereinafter referred to as ordinary light) into a test subject body for imaging the interior of the subject body by an imaging device like CCD. Recently, for the sake of acquiring such images that show the details of particular tissues or biological components of the subject body, which are not clearly perceivable from endoscopic images acquired under the ordinary light, some of the electronic endoscopes also use rays of particular narrow wavelength bands (hereinafter referred to as special light) as illumination light for the imaging.
Also, such methods for processing endoscopic images have recently been known in the art that make particular tissues conspicuous in the image by enhancing the contrast of these tissues. In an example, blood vessels in superficial mucosal layer (or superficial blood vessels) may be contrast-enhanced through an image processing procedure for enhancing those image fragments which have a particular spatial frequency within an acquired image, hereinafter referred to as frequency enhancement. Such digital image processing as the frequency enhancement is effective to improve the visibility of target tissues in combination with the endoscopic image acquired under the special light.
Generally, the endoscope is provided with a channel 28 along a probing portion that is introduced into the test subject body or patient, so that a surgical tool like forceps may be inserted through the channel 28 and protruded from a distal end of the probing portion. Thus, using the surgical tool, the operator of the endoscope may apply a surgical procedure or treatment to a target site like tumor tissues of the subject body. Since the tip of the surgical tool is protruded from the distal end of the probing portion and hence located within the view field or imaging field of the endoscope, the operator is able to operate the surgical tool to conduct the procedure while watching the images monitored by the endoscope and checking the position of the surgical tool to the target site.
The surgical tools may however cause problems when protruded into the imaging field of the endoscope. For example, some of the surgical tools may reflect the illumination light so much that the monitored endoscopic images suffer smears or flares, which will obstruct the inspection of the target site. To solve this problem, such electronic endoscopes that prevent the smears and flares by blocking the incidence of the reflected light from the surgical tool onto the imaging device have been suggested for example in JPA 2002-65586 and JPA 1991-275028.
In addition to the above problem, when endoscopic image containing the surgical tool beside the target subject is digitally processed for example for the above-mentioned frequency enhancement, if pixels corresponding to the surgical tool are processed in the same way as other pixels of the image, the image of the surgical tool may often be modified undesirably, such as being altered in color, or getting moirés or other periodic patterns, which will adversely affect the inspection of the target site. The same problem can occur when the distal end of the probing portion of the endoscope bends so sharply that the probing portion itself is pictured in the endoscopic image.
The above problem in processing endoscopic image is inevitable so long as the surgical tool is to be captured in the endoscopic image. The above method of preventing the reflected light from the surgical tool from entering the imaging device of the endoscope is not useful for solving the problem caused by the image processing.